Elevator rescue operation control system including selective transformer winding energization

ABSTRACT

A power supply for an elevator drive includes a voltage input, a comparator for comparing the input voltage with a predetermined threshold, a transformer having a primary winding and a secondary winding connected to the elevator drive. The transformer has a single tapped primary winding. When the input voltage exceeds the predetermined threshold input, the comparator output causes power to be supplied to the primary winding via one of an end of the winding or the tapping of the winding, and when the input voltage is below the predetermined threshold, input power is supplied to the primary winding via the other of the end of the primary winding and the tapping of the winding.

The present invention relates to a system for controlling operation ofan elevator in a rescue operation in the event of a power failure.

BACKGROUND

If the mains power supplying an elevator fails, the elevator will stoprunning. If the elevator is between floors, the passengers are unable toget out of the elevator and this can cause impatience and anxiety. Mostelevators are provided with an alarm button inside or outside theelevator cab which can be pressed by passengers trapped in the elevatoror people outside the elevator. This may cause an alarm to sound outsidethe elevator to alert help and/or may be connected, bytelecommunication, to a help center so that the trapped passengers cancommunicate with someone outside of the elevator and call for help. Thealarm button will have its own power supply e.g. a battery so that itremains in action even when the mains power fails.

To avoid passengers being trapped in an elevator for any length of time,many modern elevators are now provided with a back up power supply inthe form of a battery or accumulator which is switched on eitherautomatically or by pressing a button within the elevator in the eventof a mains power failure. The power from the battery is sufficient forthe elevator controller to be able to bring the elevator to the nearestfloor. When the elevator arrives at the floor the doors can be openedand the passengers can exit the elevator.

Most elevators comprise an elevator car suspended in a hoistway or shafton steel ropes or cables which run over a pulley at the top of the shaftand which are attached at the other end to a counterweight. A main motoris provided to drive the elevator car in accordance with instructionsfrom an elevator controller.

In the event of a mains power failure, the motor ceases running and thebrake is applied to prevent the elevator falling to the bottom of thehoistway or being shot up the hoistway as the counterweight falls. Thiswill result, in many cases, in the elevator being suddenly brought to astop between floors.

In some elevators, a rescue mechanism allows the brake to be released byproviding power from an emergency power supply such as a battery to thecontroller. Depending on the relative weights of the elevator car andthe counterweight the car will either move up or down until it reachesthe next floor. A sensor will detect when the elevator reaches the floorand will re-apply the brake and the doors can be opened to let thepassengers out.

US Patent Publication No. 20040020726 discloses such an emergencyoperation. When the car is trapped between floors, the passengers pressan emergency button which releases the brake allowing the car to move tothe next floor.

U.S. Pat. No. 6,264,005 also teaches such a system in which the actualspeed of the car in moving to the next floor is not (as in US2004002726) merely dependent on the difference in weight between the car(which is dependent on the passenger load) and the counterweight. Inthis patent, the rescue operation during power failure is controlled bycontrolling a speed and torque of a permanent magnet type synchronousmotor with its electricity generating power.

Both systems do, however, rely on an imbalance between the car and thecounterweight to bring the elevator to the next floor in the case of acar stopping between floors due to power failure. This means that therescue operation will not work where there is no load imbalance.Furthermore, the elevator will only be able to move in one direction(depending on the relative weights of the car and the counterweight) andwill not necessarily move to the nearest floor. If the rescue operationis also to work where there is no load imbalance drive support isrequired—i.e. a drive powered by the emergency power supply must be ableto drive the elevator to the next floor.

In all systems with a rescue operation, circuitry is provided whichallows the parts of the system needed to implement the rescue operationto be supplied with power from an emergency power supply in the event ofmains power failure. The emergency power supply is usually a battery oraccumulator. The circuitry thus usually includes a switched mode powersupply for switching from mains power to battery power.

Most such systems use an uninterruptible power supply powered bybatteries or an emergency generator. In the event of a mains powerfailure, these devices will generate the same voltage level as wasprovided by the mains supply.

Such arrangements are large and expensive, and require fairly complexcircuitry and relatively large components requiring more board space andmore connections. There is, therefore, a need for a simple, effectiveswitched mode power supply circuit which allows power supply to a drivecircuit for an elevator to switch easily from mains power to batterypower in, e.g. the event of a power failure so that the elevator can bedriven to the next floor.

SUMMARY

Accordingly, the invention comprises a power supply for an elevatordrive, comprising a voltage input, a comparator for comparing the inputvoltage with a predetermined threshold, a transformer having a primarywinding and a secondary winding connected to the elevator drive; wherethe transformer has a single tapped primary winding and wherein, whenthe input voltage exceeds the predetermined threshold input, thecomparator output causes power to be supplied to the primary winding viaone of an end of the winding or the tapping of the winding, and when theinput voltage is below the predetermined threshold, input power issupplied to the primary winding via the other of the end of the primarywinding and the tapping of the winding.

Although the present invention can operate over a wide voltage range andswitch between the two SMPS stages for any preselected drop in voltage,preferably, the voltage input comprises a mains power supply and abattery, connected to the comparator input. When the mains power supplyis functioning, the comparator outputs a signal indicating that theinput voltage exceeds the predetermined threshold. In the event of amains power failure, the input voltage to the comparator is from thebattery and this is less than the predetermined threshold.

Whilst, in theory, the invention would work if both the mains and thebattery were permanently connected to the comparator, this clearlyinvolves undesired continuous use of the battery. Thus, in a preferredembodiment the battery is connected to the comparator via a switch whichis normally open and closes when the mains power fails or falls below agiven value. The battery switch could be closed automatically ormanually by means of a passenger or a person outside the elevatorpressing a button.

Thus, the present invention provides a two stage SMPS for an elevatordrive—one stage is active during normal mains operation—the other onecan be activated when the drive is battery powered. The single SMPStransformer needs only a single tapped primary coil. The battery voltagecan be switched to the drive input and the SMPS itself will decide whichcontrol stage has to be activated.

Preferred embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows an example of a switched mode power supply according to thepresent invention.

DETAILED DESCRIPTION

The drive SMPS consists of a rectifier 1, a DC link capacitor 2, acontrol circuit and a transformer 8 having a single, tapped primarywinding. The drive circuitry to be powered by the SMPS is connected tothe transformer output. The power inverter 11 for the motor control isconnected to the rectifier and the DC link capacitor.

The control circuit comprises a comparator 3 receiving power inputsignals and comparing the input signal with a predetermined thresholdvalue. The control circuit also comprises first 4 and second 5 pulsewidth modulator units (PWM) connected to the output of the comparator.The PWM are connected to control respective first 6 and second 7 powerswitches. The first power switch is connected to one end of the primarywinding. The second power switch is connected to the other end of theprimary winding.

Under normal operation the drive circuitry is powered by the mains poweri.e. the SMPS is a mains supplied SMPS. The voltage comparator 3recognises that the input to it is mains power input and outputs asignal to enable the first PWM unit 4 which controls the first powerswitch 6. The second PWM 5 is disabled. The first power switch isconnected to one end of the tapped primary winding. The tapping of theprimary winding is connected to the positive rectified input voltage sothat there is a direct connection to the rectifier and to the DC linkcapacitor.

If the input voltage to the comparator falls below a given thresholde.g. due to mains power failure, the comparator outputs a signal whichdisables the first PWM 4 and enables the second PWM 5. The second PWMthus starts to control the second power switch 7 which is connected tothe opposite end of the primary winding to that to which the firstswitch is connected.

In the case of a mains power failure the small DC link capacitor 2discharges very quickly. The battery 10 can then be switched to theinput of the drive SMPS i.e. to the input of the comparator by a contact9. This could be actuated automatically or manually e.g. by a passengerpressing an emergency button inside the elevator, or by someone pressingan emergency button located outside the elevator, e.g. in the controllercabinet.

When mains power is restored the battery contact opens and the voltagecomparator detects the higher mains voltage and enables the first PWM.

Thus, the two stage SMPS of the present invention works over a widerange of input voltages, which cannot be achieved by a transformer withonly a single, simple winding. At low input voltages, a huge de-ratingof the transformer output power would be necessary-however, this is notacceptable for a SMPS design. Furthermore compared to previous systems,fewer mechanical contacts are required for the battery and thetransformer is much simpler and smaller. Compared to prior systems, theSMPS requires less board spaced and is simpler and, thus less expensiveto manufacture. Also the arrangement of a prior system requires anadditional connector for the transformer in the battery supply mode.

Thus, the arrangement of the present invention maintains the operatingadvantages of a circuit with two transformers whilst providing a simple,compact and less expensive design which operates over a wide range ofinput voltages.

1. A power supply for an elevator drive, comprising a voltage input, acomparator for comparing the input voltage with a predeterminedthreshold, a transformer having a single tapped primary winding and asecondary winding, the secondary winding being connected to the elevatordrive; wherein, when the input voltage exceeds the predeterminedthreshold input, an output of the comparator is configured to causepower to flow between the tapping of the primary winding and a first endof the primary winding, and wherein, when the input voltage is below thepredetermined threshold, the output of the comparator is configured tocause power to flow between the tapping of the primary winding and asecond end of the primary winding.
 2. The power supply of claim 1,wherein the voltage input comprises a mains power supply and a battery,connected to the comparator input, wherein, when the mains power supplyis functioning, the comparator outputs a signal indicating that theinput voltage exceeds the predetermined threshold, and in the event of amains power failure, the input voltage to the comparator is from thebattery and this is less than the predetermined threshold.
 3. The powersupply of claim 1, wherein the battery is connected to the comparatorvia a switch which is normally open and closes when the mains powerfails or falls below a given value.
 4. The power supply of claim 3,wherein the switch closes automatically when the mains power fails orfalls below a given value.
 5. The power supply of claim 3, wherein theswitch is adapted to be closed manually by means of pressing a button.